1. Field of the Invention
The present invention pertains to compositions for inhibiting stress cracking in poly(alkylene terephthalate) articles of manufacture. More particularly, the present invention concerns aqueous-based bottle washing compositions containing such stress crack inhibitors. Even more particularly, the present invention concerns caustic aqueous concentrates and bottle washing use solutions therefor which contain such stress crack inhibitors, and methods of washing poly(alkylene terephthalate) articles using the compositions hereof.
2. Prior Art
As is known to those skilled in the art to which the present invention pertains, there has been an ever increasing usage of synthetic resinous containers for storing fluids and solids. Likewise, as is known to those skilled in the art, such containers are normally filled or washed by passing them through filling and capping stations along manually, mechanically or electronically operated conveyor systems. Likewise, such containers are normally washed by passing them through a washing system along manually, mechanically or electronically-operated conveyor systems.
When poly(alkylene terephthalate) articles are washed for recycling and reuse thereof, highly caustic detergent solutions are normally used to remove old labels and to clean and sterilize the interior of the articles. However, these known cleaning compositions tend to attack and degrade the poly(alkylene terephthalate) making up the articles, which can lead to "stress cracks" within, or even completely through, the walls of the articles over repeated washing cycles. Typically, conventional caustic bottle washing compositions may, also, contain other constituents which have a deleterious effect on the poly(alkylene terephthalate) article disposed along the conveyor system.
Indeed, it has long been known that exposure by such articles to these compositions leads to these phenomenon which has been identified as "stress cracking" in these poly(alkylene terephthalate) containers and other such articles of manufacture. This is true with respect to both poly(ethylene terephthalate) and poly(butylene terephthalate) containers. The stress cracking phenomenon is also noted in polycarbonate articles of manufacture. Mild stress cracking which "fogs" the normally transparent PET material and which extends only partially through the wall of an article is commonly referred to as "hazing".
As noted, conventional aqueous-based bottle washing compositions containing caustics, alcohols nonionic surfactants and/or other additives do not inhibit or prevent stress cracking in such containers, but rather, promote stress cracking.
In U.S. Pat. No. 4,929,375 there is disclosed a highly dilutable aqueous lubricant concentrate which appears to inhibit stress cracking by combining a tertiary alkyl amine as a saponifying agent and an alkyl aryl sulfonate, as a solubilizing agent for a long chain fatty acid. While the compositions of the patent are efficacious for preparing highly dilutable lubricants, it has been found that the tertiary amine, per se, is not always essential to stress crack inhibition.
Rather, it has now been found that a certain class of alkyl aryl sulfonates and other hydrophile-terminated aromatic compounds, when added to a caustic bottle washing composition, either alone or in combination with free-base amines, will inhibit stress cracking when formulated into a bottle washing system. This finding enables the production of dilutable, cost efficient, caustic aqueous bottle washing compositions without any dilatory effects caused by the presence of the amine. Likewise, this finding enables implementation of other means and methods for inhibiting stress cracking in poly(alkylene terephthalate) articles other than the above-referred to copending applications and issued patents.
Heretofore, the only proposed method of inhibiting stress cracking in plastic bottles known to the applicants, has been the incorporation of an alkali metal salt of a hydrophilic substituted aromatic hydrocarbon and other hydrotropes into a liquid bleach, such as disclosed in European Patent Application No. EP 302705 A2, filed Feb. 8, 1989. This application discloses the use of the hydrotropes in an adjustment to the bleach to inhibit stress cracking in high density polyethylene containers. Yet, the art has not directed itself to bottle washing compositions and other media for inhibiting stress cracking in polyethylene or polybutylene terephthalate bottles or other articles of manufacture, such as polycarbonate articles.
U.S. Pat. No. 4,769,162 to Remus discloses a water soluble conveyor lubricant concentrate which includes an anionic surfactant and a water-soluble aluminum salt. The disclosure of Remus U.S. Pat. No. '162 is not directed to a bottle washing composition, per se.